Apparatus for energy transfer using converter and method of manufacturing same

ABSTRACT

According to an aspect of the invention, a motor drive circuit includes a first energy storage device configured to supply electrical energy, a bi-directional DC-to-DC voltage converter coupled to the first energy storage device, a voltage inverter coupled to the bi-directional DC-to-DC voltage converter, and an input device configured to receive electrical energy from an external energy source. The motor drive circuit further includes a coupling system coupled to the input device, to the first energy storage device, and to the bi-directional DC-to-DC voltage converter. The coupling system has a first configuration configured to transfer electrical energy to the first energy storage device via the bi-directional DC-to-DC voltage converter, and has a second configuration configured to transfer electrical energy from the first energy storage device to the voltage inverter via the bi-directional DC-to-DC voltage converter.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of and claims priority to U.S.patent application Ser. No. 13/406,241 filed Feb. 27, 2012 which is acontinuation of and claims priority to U.S. patent application Ser. No.13/314,572 filed Dec. 8, 2011 and issues as U.S. Pat. No. 9,227,523,which is a continuation of and claims priority to U.S. patentapplication Ser. No. 12/256,466 filed Oct. 22, 2008 and issues as U.S.Pat. No. 8,080,973, the disclosures of which are incorporated herein.

BACKGROUND OF THE INVENTION

The invention relates generally to hybrid and electric vehicles, andmore specifically to systems for charging the energy storage devicesused for powering hybrid and electric vehicles.

Hybrid electric vehicles combine an internal combustion engine and anelectric motor that is typically powered by an energy storage device,such as a traction battery. Such a combination may increase overall fuelefficiency by enabling the combustion engine and the electric motor toeach operate in respective ranges of increased efficiency. Electricmotors, for example, may be efficient at accelerating from a standingstart, while combustion engines may be efficient during sustainedperiods of constant engine operation, such as in highway driving. Havingan electric motor to boost initial acceleration allows combustionengines in hybrid vehicles to be smaller and more fuel efficient.

Purely electric vehicles typically use stored electrical energy to poweran electric motor, which propels the vehicle. Purely electric vehiclesmay use one or more sources of stored electrical energy. For example, afirst source of stored electrical energy may be used to providelonger-lasting energy while a second source of stored electrical energymay be used to provide higher-power energy for, for example,acceleration.

Plug-in hybrid electric vehicles are configured to use electrical energyfrom an external source to recharge the traction battery. This savesfuel by reducing the amount of time the internal combustion engine mustoperate to recharge the traction battery. Such vehicles, which mayinclude on-road and off-road vehicles, golf carts, forklifts and utilitytrucks may use either off-board stationary battery chargers or on-boardbattery chargers to transfer electrical energy from an external energysource, such as the utility grid, to the vehicle's on-board tractionbattery. Plug-in hybrid passenger vehicles typically include circuitryand connections to facilitate the recharging of the traction batteryfrom an external energy source, such as the utility grid, for example.Typically, the battery charging circuitry includes boost converters,high-frequency filters, choppers, inductors and other electricalcomponents. These additional components which are not generally usedduring vehicle operation add cost and weight to the vehicle.

It would therefore be desirable to provide an apparatus to facilitatethe transfer of electrical energy from an external source to theon-board electrical storage device of a plug-in vehicle that reduces thenumber of components dedicated only to transferring energy between theon-board electrical storage device and the external source.

BRIEF DESCRIPTION OF THE INVENTION

According to an aspect of the invention, a motor drive circuit includesa first energy storage device configured to supply electrical energy, abi-directional DC-to-DC voltage converter coupled to the first energystorage device, a voltage inverter coupled to the bi-directionalDC-to-DC voltage converter, and an input device configured to receiveelectrical energy from an external energy source. The motor drivecircuit further includes a coupling system coupled to the input device,to the first energy storage device, and to the bi-directional DC-to-DCvoltage converter. The coupling system has a first configurationconfigured to transfer electrical energy to the first energy storagedevice via the bi-directional DC-to-DC voltage converter, and has asecond configuration configured to transfer electrical energy from thefirst energy storage device to the voltage inverter via thebi-directional DC-to-DC voltage converter.

In accordance with another aspect of the invention, a method ofmanufacturing that includes providing a first energy storage device,coupling a first bi-directional buck/boost converter to the first energystorage device, and coupling an input device to the first bi-directionalbuck/boost converter. The input device is configured to receiveelectrical energy from an external energy source. The method furtherincludes coupling one or more coupling devices to the firstbi-directional buck/boost converter, to the first energy storage device,and to the input device, the one or more coupling devices configured tocause electrical energy to charge the first energy storage device viathe first bi-directional buck/boost converter, and configured to causeelectrical energy from the first energy storage device to transfer tothe voltage inverter via the first bi-directional buck/boost converter.

According to yet another aspect of the invention, a traction systemincludes an electric motor configured to propel a vehicle and a voltageinverter configured to supply an AC power signal to the electric motor.The system also includes a motor drive circuit configured to supply a DCpower signal to the voltage inverter. The motor drive circuit has afirst battery and a first bi-directional buck/boost converter coupled tothe first battery, the first bi-directional buck/boost converter havinga first inductor and a first transistor. The motor drive circuit alsohas an input device configured to receive electrical energy from anexternal energy source and has a coupling system having a firstconfiguration in which the external energy source is coupled to thefirst battery via the input device and the first bi-directionalbuck/boost converter. The coupling system also has a secondconfiguration in which the first battery is coupled to the voltageinverter via the first bi-directional buck/boost converter.

Various other features and advantages will be made apparent from thefollowing detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate embodiments presently contemplated for carryingout the invention.

In the drawings:

FIG. 1 is a schematic diagram illustrating a traction system accordingto an embodiment of the invention.

FIG. 2 is a schematic diagram illustrating a traction system accordingto another embodiment of the invention.

FIG. 3 is a schematic diagram illustrating a traction system accordingto another embodiment of the invention.

FIG. 4 is a schematic diagram illustrating a traction system accordingto another embodiment of the invention.

FIG. 5 is a schematic diagram illustrating a traction system accordingto another embodiment of the invention.

FIG. 6 is an alternate embodiment of the traction system illustrated inFIG. 5 according to another embodiment of the invention.

FIG. 7 is a schematic diagram illustrating a traction system accordingto another embodiment of the invention.

FIG. 8 is a schematic diagram illustrating a traction system accordingto another embodiment of the invention.

FIG. 9 is a schematic diagram illustrating a traction system accordingto an embodiment of the invention.

DETAILED DESCRIPTION

In an embodiment of the invention illustrated in FIG. 1, a tractionsystem 100 usable in a vehicle, such as a plug-in electric or plug-inhybrid vehicle, or stationary electric drive system is shown. Tractionsystem 100 includes a first energy storage device 102, which may be abattery, a fuel cell, an ultracapacitor, or the like, coupled to aninductor 104 of a bi-directional DC-to-DC voltage converter 106.Inductor 104 is coupled to a first transistor 108 and a secondtransistor 110 connected in series. Each of the transistors 108, 110 iscoupled in anti-parallel with a first and second diode 112, 114,respectively. A coupling system 116 includes a switch 118, which may be,for example, a contactor, a relay, a semiconductor switch, or the like.Switch 118 has a first position 120 and a second position 122 and iscoupled to first transistor 108. When switch 118 is in first position120, bi-directional DC-to-DC voltage converter 106 is coupled to aninput device 124, which includes a diode rectifier 126 and a receptacle128, 129 configured to connect to an electrical plug 130, 131 of anexternal energy source 132 for transfer of DC or AC electrical energy.In an embodiment of the invention, an electrical cord 133 incorporatingplug 130, 131 may be coupled to an outlet (not shown) coupled toexternal energy source 132 to electrically connect external energysource 132 to input device 124 for transfer of DC or AC electricalenergy. External energy source 132 may be, for example, a utility grid.When switch 118 is in second position 122, bi-directional DC-to-DCvoltage converter 106 is coupled to a three-phase DC-to-AC voltageinverter 134, which inverts DC power into AC power for driving anelectric motor 136. Embodiments of the invention are not limited tothree-phase voltage inverters and may include voltage inverters with agreater or lesser number of phases.

In an embodiment of the invention, a second energy storage device 138(shown in phantom), which may be a battery, a fuel cell, anultracapacitor, or the like, is coupled to voltage inverter 134.Bi-directional DC-to-DC voltage converter 106 may be a bi-directionalbuck/boost converter. As such, bi-directional buck/boost converter 106may include a capacitor 140 (shown in phantom) coupled across the twotransistors 108, 110. When charging energy storage devices 102, 138using voltage from an external energy source 132, bi-directionalDC-to-DC voltage converter 106 permits modulation or buck conversion ofthe voltage to control the energy transfer between external energysource 132 and energy storage devices 102, 138. An increase in the powerfactor compared to conventional battery chargers results in a moreefficient transfer of energy to the storage devices 102, 138.

The power factor of an AC electric power system is defined as the ratioof the real power to the apparent power and may be expressed as a numberbetween 0 and 1 or as a percentage between 0 and 100. Real power is thecapacity of the circuit for performing work in a particular time.Apparent power is the product of the current and voltage of the circuit.Due to energy stored in the load and returned to the source, or due to anon-linear load that distorts the wave shape of the current drawn fromthe source, the apparent power can be greater than the real power. Acircuit with a lower power factor performs less work than a circuit witha higher power factor. Therefore, to perform the same amount of work, ahigher voltage or current is input into the circuit with the lower powerfactor.

In circuits having sinusoidal currents and voltages, the power factormay be decreased due to differences in phase between the current andvoltage. Switch-mode power supplies may be configured to control theamount of power drawn by a load to increase the energy transfer powerfactor. In some applications, a switch-mode power supply, such as oneincluding a buck/boost converter for example, controls the currentoutput therefrom so that the current waveform is proportional to thevoltage waveform output therefrom. For example, the buck/boost convertermay shape the current waveform into a sine wave that is in phase with asine wave of the voltage waveform. The boost converter can be controlledto maintain a constant DC bus output line voltage while drawing acurrent that is in phase with, and at the same frequency as, the outputline voltage.

In operation, switch 118 is placed in second position 122 during normalvehicle operation (i.e., motoring). First energy storage device 102supplies a DC voltage to bi-directional DC-to-DC voltage converter 106,which steps up, or boosts, the DC voltage. The boosted DC voltage isconverted into an AC voltage by voltage inverter 134 to drive electricmotor 136. Likewise, during normal vehicle operation (i.e. decelerationor while braking, often referred to as regenerative braking), electricdrive motor 136 acts as an electrical generator and an AC voltage isconverted to a DC voltage in the voltage inverter 134 and supplies a DCvoltage to bi-directional DC-to-DC voltage converter 106, which stepsdown, or bucks, the DC voltage and supplies the DC voltage to partiallyrecharge the first energy storage device 102.

Switch 118 is placed in first position 120 during recharging of firstenergy storage device 102 from the external source 132. Plug 130, 131transfers power from external energy source 132, such as the utilitygrid, through receptacle 128, 129 to diode rectifier 126. In anembodiment of the invention, diode rectifier 126 converts an AC voltageinto a DC voltage, which generates an electric current that chargesfirst energy storage device 102 through first transistor 108, seconddiode 114, and inductor 104. By toggling switch 118 to second position122, first energy storage device 102 supplies a DC voltage tobi-directional DC-to-DC voltage converter 106, which boosts the DCvoltage and supplies the boosted DC voltage to charge second energystorage device 138 through switch 118.

An embodiment of the invention illustrated in FIG. 2 shows a tractionsystem 142 usable in a vehicle, such as a plug-in electric or plug-inhybrid vehicle, or stationary electric drive system. Elements andcomponents common to traction systems 100 and 142 will be discussedrelative to the same reference numbers as appropriate. FIGS. 3-8 willalso discuss common components relative to the same reference numbers.Switch 118, rather than being directly coupled to first transistor 108as shown in FIG. 1, is directly coupled to inductor 104 ofbi-directional DC-to-DC voltage converter 106. In a first position 144,switch 118 couples bi-directional DC-to-DC converter 106 to first energystorage device 102. In a second position 146, switch 118 couplesbi-directional converter 106 to input device 124.

In operation, switch 118 is placed in first position 144 during normalvehicle operation (i.e., motoring or regenerative braking). As in theembodiment described with respect to FIG. 1, during motoring, firstenergy storage device 102 supplies a DC voltage to bi-directionalDC-to-DC voltage converter 106, which steps up, or boosts, the DCvoltage that is then output to second energy storage device 136 andconverted into an AC voltage by voltage inverter 134 to drive theelectric motor 136. Similar to FIG. 1, during regenerative braking,motor 136 acts as a generator and electrical energy and power aretransferred through inverter 134, to partially recharge second energystorage device 138, if present, plus transfer of electrical energy andpower through bi-directional DC-DC converter 106, (acting in buck mode)to partially recharge first energy storage device 102.

Placing switch 118 in second position 146 couples inductor 104 to inputdevice 124. Diode rectifier 126 provides a DC charging signal tobi-directional DC-to-DC voltage converter 106, which outputs a boostedcharging DC signal to charge second energy storage device 138. Bytoggling switch 118 to first position 144, electrical energy can betransferred from second energy storage device 138 through firsttransistor 108, diode 114 and inductor 104 to charge first energystorage device 102.

An embodiment of the invention illustrated in FIG. 3 includes a tractionsystem 148 usable in a vehicle, such as a plug-in electric or plug-inhybrid vehicle, or other stationary electric drive system. In thisembodiment, coupling system 116 includes a first, second, and thirdcontactor 150, 152, and 154, respectively. First energy storage device102 is directly coupleable to inductor 104 through first contactor 150and directly coupleable to first transistor 108 through a secondcontactor 152. First transistor 108 is directly coupleable to secondenergy storage device 138 through a third contactor 154.

In operation, first energy storage device 102 is charged when secondcontactor 152 is closed and the other two contactors 150, 154 are open.Electrical energy from external energy source 132 flows through inductor104, first contactor 152, and the bidirectional converter 106, whichacts as a boost converter to charge first energy storage device 102.When in this boost mode, transistor 110 switches at a high frequency andinverse diode 112 acts as a “freewheeling” diode. Second energy storagedevice 138, if present, is charged when third contactor 154 is closedand the other two contactors 150, 152 are open. In one example,electrical energy from the utility grid, converted to a DC signal bydiode rectifier 126, flows through inductor 104, third contactor 154 andthe bidirectional DC-to-DC voltage converter 106 acts as a boostconverter to charge second energy storage device 138. It is contemplatedthat first and second energy storage devices 102, 138 may besimultaneously charged by closing second and third contactors 152, 154and opening second contactor 150.

When the vehicle is in motoring mode, contactors 150 and 154 are closedand the other contactor 152, is open. During motoring, first energystorage device 102 supplies a DC voltage through the contactor 150 tobi-directional DC-to-DC voltage converter 106 which boosts the DCsignal. The DC power signal from converter 106 flows through the thirdcontactor 154. DC power from converter 106 and second energy storagedevice 138 is converted into an AC signal by voltage inverter 134 todrive electric motor 136. Operation during regenerative braking issimilar as described above, where bi-directional DC-to-DC voltageconverter 106 bucks the higher voltage from the DC side of the DC-to-ACvoltage inverter 134 to the lower voltage to partially charge the firstenergy storage device 102.

An embodiment of the invention illustrated in FIG. 4 shows a tractionsystem 156 usable in a vehicle, such as a plug-in electric or plug-inhybrid vehicle, or stationary electric drive system. Traction system 156includes a first, second, and third bi-directional DC-to-DC voltageconverter 158, 160, 162 coupled in parallel. Converters 158-162respectively include a first, second, and third inductor 164, 166, 168of traction system 156. Converter 158 includes a first and secondtransistor 170, 172 and a first and second diode 174, 176 of tractionsystem 156. Converter 160 includes a third and fourth transistor 178,180 and a third and fourth diode 182, 184 of traction system 156.Converter 162 includes a fifth and sixth transistor 186, 188 and a fifthand sixth diode 190, 192 of traction system 156. Each transistor 170,172, 178, 180, 186, 188 is coupled in anti-parallel with a respectivediode 174, 176, 182, 184, 190, 192. Each of the bi-directional DC-to-DCvoltage converters 158-162 may be a bi-directional buck/boost converter.

Coupling system 116 includes a first, second, and third contactor 194,196, and 198, respectively. First energy storage device 102 is directlycoupleable to second inductor 166, to third inductor 168, and to firstinductor 164 through first contactor 194. Second contactor 196 iscoupled between first transistor 170 and first energy storage device102. Third contactor 198 is coupled between first transistor 170 andthree-phase voltage inverter 134, which is coupled to electric motor136.

In operation, first energy storage device 102 is charged when secondcontactor 196 is closed and the other two contactors 194, 198 are open.External energy source 132 provides a DC power signal or an AC powersignal, for example from the utility grid, which is converted into a DCsignal by diode rectifier 126. The DC signal flows through inductor 164,first contactor 196 and bidirectional DC-to-DC voltage converter 158 tofirst energy storage device 102.

Second energy storage device 138, if present is charged when thirdcontactor 198 is closed and the other two contactors 194, 196 are open.In this case, an AC power signal, as might be provided by the utilitygrid, is converted to a DC signal by diode rectifier 126. The DC signalflows through bi-directional DC-to-DC voltage converter 158 (firstinductor 164, second transistor 172, first diode 174) and through thirdcontactor 198 to second energy storage device 138. When the vehicle ismotoring, second contactor 196 is open and the other two contactors 194,198 are closed. In this mode, first energy storage device 102 supplies aDC signal to each of the inductors 166, 168, 164 of the respectivebi-directional DC-to-DC voltage converters 158, 160, 162. Each of thethree voltage converters 158, 160, 162 boosts the DC signal from firstenergy storage device 102 and outputs the boosted voltage to voltageinverter 134, where the resulting DC signal is converted into an ACsignal suitable for driving electric motor 136. One or all of the boostconverters may be used depending on the power needed. If low power isneeded, only one of the converters can be used to increase overall partload efficiency. When more than one converter is used, their switchingmay be interleaved to increase the effective switching frequency andthereby reduce ripple current and voltage on first energy storage device102 and any other DC bus filters (not shown). Operation duringregenerative braking is similar as described above, where bi-directionalDC-to-DC voltage converters 158, 160, 162 are operated in a buck mode toreduce the voltage generated by motor 136 after passing through voltageinverter 134.

An embodiment of the invention illustrated in FIG. 5 shows an embodimentof a traction system 200 usable in a vehicle, such as a plug-in electricor plug-in hybrid vehicle, or other stationary electric drive system.Coupling system 116 includes a first, second, third, and fourthcontactor 202, 204, 206, 208. First energy storage device 102 isdirectly coupleable to first inductor 164 through first contactor 202and to second inductor 166 through second contactor 204. First energystorage device 102 is directly coupled to third inductor 168. Outputs ofthe three bi-directional DC-to-DC voltage converters 158, 160, 162 arecoupled to voltage inverter 134, which is, in turn, coupled to electricmotor 136. Input device 124 having receptacle 128, 129 for a plug 130,131 is configured to receive electrical power from external energysource 132, which may be an external AC power source, such as theutility grid. One terminal of input device 124 is directly coupleable tosecond inductor 166 through fourth contactor 208, and the secondterminal of input device 124 is directly coupleable to first inductor164 through third contactor 206.

In an alternate embodiment of the invention, input device 124 furtherincludes a transformer 210 (shown in phantom) to isolate system 200 fromexternal energy source 132. Typically, electrical outlets provide 120volts AC or 240 volts AC. Transformer 210 could be configured to step upthe utility grid voltage at input device 124 from 120 Vac or 240 Vac to480 Vac or higher. The higher voltage allows for faster charging ofenergy storage devices 102, 132.

In operation, both first energy storage device 102 and second energystorage device 138 are charged when the third and fourth contactors 206,208 are closed and the first and second contactors 202, 204 are open.External energy source 132 provides a voltage to system 200 at inputdevice 124. With no rectifier, the first and second bi-directionalvoltage converters 158, 160 are used to convert an AC input voltage intoa DC voltage via an AC source coupled between to full bridge phase legs,comprised of transistors 178, 180 in one phase leg and 170 and 172 inthe second phase leg. Note, the operation of two phase legs in the twobi-directional DC-DC converters 158, 160 is similar to operation of twoof the three phase legs of DC-to-AC voltage inverter 134 duringregenerative braking mode when electric motor 136 generates an ACvoltage and voltage inverter 134 produces a DC voltage.

When the vehicle is motoring, the first and second contactors 202, 204are closed and the third and fourth contactors 206, 208 are open. Inthis case, closing the first and second contactors 202, 204 results incoupling first energy storage device 102 to the first, second and thirdinductors 164, 166, 168 of the respective bi-directional DC-to-DCvoltage converters 158, 160, 162. Converters 158, 160, 162 boost the DCvoltage from first energy storage device 102 and output the boosted DCvoltage to voltage inverter 134 and to second energy storage device 138,if present. Voltage inverter 134 converts the DC voltage into an ACvoltage suitable for driving electric motor 136.

FIG. 6 shows an alternate embodiment of traction system 200 illustratedin FIG. 5. In this embodiment, external energy source 132 is a DC powersource and utilizes either a single bi-directional DC-DC converter, forexample either 160 or 158, or for higher power charging applications,utilizes two bi-directional DC-to-DC voltage converters 160, 158 in aparallel mode using asynchronous and staggered switching toadvantageously minimize ripple current to further increase chargerefficiency. A first positive terminal 205 of DC power source 132 isdirectly connected, through plug 130, 131 and receptacle 128, 129, to acontactor such as contactor 208 as shown for single DC-to-DC boostconverter operation. Positive terminal 205, however, may instead beconnected to contactor 206 (as shown in phantom) for single DC-to-DCboost converter operation. For higher power operation, positive terminal205 may be connected, through plug 130, 131 and receptacle 128, 129, toboth contactors 208 and 206. A negative terminal 209 of DC power source132 is directly connected, through plug 131 and receptacle 129, to acommon line 211 of traction system 200.

For charging of first energy storage device 102 and, if present, secondenergy storage device 138, first positive terminal 205 supplies DC powerthrough contactor 208 to second bi-directional DC-to-DC voltageconverter 160. If contactor 206 is also connected to first positiveterminal 205, DC power is supplied to first bi-directional DC-to-DCvoltage converter 158. DC power flows directly to second energy storagedevice 138, and through transistor 186 and inductor 168 to first energystorage device 102.

When the vehicle is motoring, contactor 204 and contactor 202, ifpresent, are closed and contactor 208 and contactor 206, if present, areopen. In this case, closing contactors 202, 204 results in couplingfirst energy storage device 102 to the first, second and third inductors164, 166, 168 of the respective bi-directional DC-to-DC voltageconverters 158, 160, 162. Converters 158, 160, 162 boost the DC voltagefrom first energy storage device 102 and output the boosted DC voltageto voltage inverter 134 and to second energy storage device 138, ifpresent. Voltage inverter 134 converts the DC voltage into an AC voltagesuitable for driving electric motor 136.

An embodiment of the invention illustrated in FIG. 7 shows a tractionsystem 212 usable in a vehicle, such as a plug-in electric or plug-inhybrid vehicle, or stationary electric drive system. Coupling system 116includes a first, second, third, and fourth contactor 214, 216, 218,220. First energy storage device 102 is directly coupleable to firstinductor 164 through first contactor 214 and to second inductor 166through second contactor 216. First energy storage device 102 isdirectly coupled to third inductor 168. Outputs of the threebi-directional DC-to-DC voltage converters 158, 160, 162 are coupled tovoltage inverter 134 which is, in turn, coupled to electric motor 136.Input device 124 has an isolation transformer 222, rather than dioderectifier 126, coupled to receptacle 128, 129. Isolation transformer 222includes a first inductor winding 224 and a second inductor winding 226.Second inductor winding 226 is directly coupleable, through thirdcontactor 218, to a node 228 between first and second transistors 170,172 of first bi-directional DC-to-DC voltage converter 158. Secondinductor winding 226 is also directly coupleable, through a fourthcontactor 220, to a node 230 between third and fourth transistors 178,180 of second bi-directional DC-to-DC voltage converter 160. In thisembodiment, transformer winding inductance is used instead ofbidirectional DC-DC converter inductors 164, 166 as shown in FIG. 5,during charging operation of first energy storage device 102 and secondenergy storage device 138, if present, with connection to external ACpower source 132.

In operation, both first energy storage device 102 and second energystorage device 138, if present, are charged when the third and fourthcontactors 218, 220 are closed and the first and second contactors 214,216 are open. Depending on the configuration of isolation transformer222 and inductor windings 224, 226, the voltage from external energysource 132 through input device 124 may be 120 Vac, 240 Vac, 480 Vac, orsome higher voltage. Operation of the two full phase legs frombi-directional DC-to-DC voltage converters 160, 158 convert the ACvoltage applied to the mid-point of the full phase transistor bridgecircuits using the transformer winding inductance is similar tooperation of DC-to-AC voltage inverter 134 during regenerative brakingoperation when the AC voltage from motor 136 is converted to a DCvoltage at inverter 134. That same DC voltage is also supplied to fifthtransistor 186 and third inductor 168 of third bi-directional DC-to-DCvoltage converter 162 to charge first energy storage device 102 usingthe bi-directional DC-to-DC voltage converter 162 in a buck mode ofoperation.

When the vehicle or stationary electric drive system is motoring, thefirst and second contactors 214, 216 are closed and the third and fourthcontactors 218, 220 are open. First energy storage device 102 supplies aDC voltage to first inductor 164 through first contactor 220, and tosecond inductor 166 through second contactor 216, and to third inductor168 directly. The three bi-directional DC-to-DC voltage converters 158,160, 162 boost the DC voltage and supply the boosted voltage to voltageinverter 134 which converts the DC voltage into an AC voltage suitablefor driving electric motor 136.

An embodiment of the invention illustrated in FIG. 8 shows a tractionsystem 232 usable in a vehicle, such as a plug-in electric or plug-inhybrid vehicle, or stationary electric drive system. Coupling system 116includes a contactor 234. First energy storage device 102 is directlycoupleable to first inductor 164 through contactor 234 and is directlycoupled to second and third inductors 166, 168. Input device 124includes a power bus 236 coupling receptacle 128, 129 to firstbi-directional DC-to-DC voltage converter 158. In an embodiment of theinvention, input device 124 includes diode rectifier 126 and optionaltransformer 222 (shown in phantom) which is coupled to receptacle 128,129.

In operation, first energy storage device 102 is charged by openingcontactor 234 to remove a direct parallel connection between firstenergy storage device 102 and input device 124. Second energy storagedevice 138 is charged by bidirectional DC-to-DC voltage converter 158operating in boost mode. Storage device 102 can be chargedsimultaneously by either or both of bidirectional DC-to-DC voltageconverters 160 and 162 operating in buck mode. In one embodiment,external power source 132 provides an AC voltage to input device 124,where the signal is converted into a DC voltage by diode rectifier 126.In an alternate embodiment of the invention, external energy source 132is a DC power source and supplies a DC voltage to input device 124. TheDC signal from diode rectifier 126 flows through first inductor 164,first transistor 170 and first diode 174 to second energy storage device138. First energy storage device 102 can be charged through either,second inductor 166 and third transistor 178, or through third inductor168 and fifth transistors 186.

When the vehicle is motoring, or the stationary electric drive is notconnected to the external source 132, contactor 234 is closed, andreceptacle 128, 129 is disengaged from plug 130, 131. First energystorage 102 device supplies a DC voltage to the first, second and thirdinductors 164, 166, 168 of the first, second and third bi-directionalDC-to-DC voltage converters 158, 160, 162 to boost the DC voltage. Theboosted DC voltage is output to voltage inverter 134, which converts theDC voltage into an AC voltage suitable for driving electric motor 136.

An alternate embodiment of system 232 includes isolation transformer 222(shown in phantom) coupled to diode rectifier 126 of input device 124.Depending on its configuration, transformer 222 can step up the voltagesupplied by external energy source 132. Increasing the input voltageinto system 232 may reduce the time needed to charge energy storagedevices 102, 138.

An embodiment of the invention illustrated in FIG. 9 shows a tractionsystem 238 usable in a vehicle, such as a plug-in electric or plug-inhybrid vehicle, or a stationary electric drive system. First and fifthtransistors 170, 186 are directly coupled to second energy storagedevice 138. Coupling system 116 includes a first and second contactor240, 242. Third transistor 178 is directly coupleable to second energystorage device 138 through first contactor 240. First storage device 102is directly coupleable to first and second inductors 164, 166 throughsecond contactor 242 and is coupled to third inductor 168 directly.Input device 124 includes diode rectifier 126 and receptacle 128, 129for electric plug 130, 131 and is configured to receive electricalenergy from external energy source 132.

In operation, second energy storage device 138, if present, is chargedby opening first and second contactors 240, 242. If second energystorage device 138 is not present, a large DC link filter capacitor (notshown) associated with the DC-to-AC voltage inverter 134 that performs aDC link filtering or smoothing function allows the DC input voltage atinverter 134 to be filtered, and the value of the voltage is regulatedin part by the power used to charge first energy storage device 102through bi-directional DC-to-DC voltage converter 162. External energysource 132 supplies an input voltage to system 238 through input device124. If necessary (i.e., if external energy source 132 is an AC energysource), diode rectifier 126 converts an AC input voltage into a DCsignal. In buck mode (i.e., instantaneous input voltage is higher thanthe voltage of second energy storage device 138), electrical energy frominput device 124 is supplied through third switching transistor 178,first and second inductors 164, 166 first and fourth diodes 174, 184(the freewheel diode), to second energy storage device 138. In boostmode (i.e., instantaneous input voltage is below the voltage of energystorage device 138), transistor 178 continuously conducts and secondtransistor 172 is switched to regulate the output of firstbi-directional DC-to-DC voltage converter, 158. Electrical energy frominput device 124 is supplied through third transistor 178, first andsecond inductors 164, 166, first diode 174, to second energy storagedevice 138. Generally, the output voltage from first and secondbi-directional DC-to-DC voltage converters 158, 160 is controlled andset at a level that maximizes an energy transfer power factor betweenexternal energy source 132 and second energy storage device 138. Energyis transferred from second energy storage device 138 to charge firstenergy storage device 102 through third bi-directional DC-to-DC voltageconverter 162. Electrical energy flows through switching fifthtransistor 186, freewheeling sixth diode 192 and third inductor 168 tocharge first energy storage device 102. It is noted that thisarrangement allows for both bucking and boosting of the input source andtherefore allows near sinusoidal current to be drawn from the input ACline (thus achieving high power factor) independent of the AC inputvoltage level. In addition, any practical DC source voltage can beaccommodated since the converters 158, 160 can either buck or boostresulting in an extremely flexible charging system.

During motoring, first and second contactors 240, 242 are closed. Firstenergy storage device 102 supplies a DC voltage to first and secondbi-directional DC-to-DC voltage converters 158, 160 through secondcontactor 242, and to third bi-directional DC-to-DC voltage converter162 directly. Each of the bi-directional DC-to-DC voltage converters158, 160, 162 boosts the DC voltage from first energy storage device 102and outputs the boosted voltage to voltage inverter 134, which convertsthe DC voltage into an AC voltage suitable for driving electric motor136. One or all of the boost converters may be used depending on thepower needed. If low power is needed, only one of the converters can beused to increase overall part load efficiency. When more than oneconverter is used, their switching may be interleaved to increase theeffective switching frequency and thereby reduce ripple current andvoltage on first energy storage device 102 and any other DC bus filters(not shown).

According to one embodiment of the invention, a motor drive circuitincludes a first energy storage device configured to supply electricalenergy, a bi-directional DC-to-DC voltage converter coupled to the firstenergy storage device, a voltage inverter coupled to the bi-directionalDC-to-DC voltage converter, and an input device configured to receiveelectrical energy from an external energy source. The motor drivecircuit further includes a coupling system coupled to the input device,to the first energy storage device, and to the bi-directional DC-to-DCvoltage converter. The coupling system has a first configurationconfigured to transfer electrical energy to the first energy storagedevice via the bi-directional DC-to-DC voltage converter, and has asecond configuration configured to transfer electrical energy from thefirst energy storage device to the voltage inverter via thebi-directional DC-to-DC voltage converter.

In accordance with another embodiment of the invention, a method ofmanufacturing that includes providing a first energy storage device,coupling a first bi-directional buck/boost converter to the first energystorage device, and coupling an input device to the first bi-directionalbuck/boost converter. The input device is configured to receiveelectrical energy from an external energy source. The method furtherincludes coupling one or more coupling devices to the firstbi-directional buck/boost converter, to the first energy storage device,and to the input device, the one or more coupling devices configured tocause electrical energy to charge the first energy storage device viathe first bi-directional buck/boost converter, and configured to causeelectrical energy from the first energy storage device to transfer tothe voltage inverter via the first bi-directional buck/boost converter.

In accordance with yet another embodiment of the invention, a tractionsystem includes an electric motor configured to propel a vehicle and avoltage inverter configured to supply an AC power signal to the electricmotor. The system also includes a motor drive circuit configured tosupply a DC power signal to the voltage inverter. The motor drivecircuit has a first battery and a first bi-directional buck/boostconverter coupled to the first battery, the first bi-directionalbuck/boost converter having a first inductor and a first transistor. Themotor drive circuit also has an input device configured to receiveelectrical energy from an external energy source and has a couplingsystem having a first configuration in which the external energy sourceis coupled to the first battery via the input device and the firstbi-directional buck/boost converter. The coupling system also has asecond configuration in which the first battery is coupled to thevoltage inverter via the first bi-directional buck/boost converter.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

What is claimed is:
 1. A vehicle charging system for a hybrid electricvehicle, the vehicle charging system comprising: a connection systemcoupleable to an external charging source, the connection systemconfigured to utilize a first connection and a second connection; aplurality of DC converters on-board the vehicle and coupleable to theconnection system, the plurality of DC converters configured to operatein combination to step up and step down an input voltage derived fromthe external charging source; an energy storage device coupleable to atleast one of the plurality of DC converters; and a controller programmedto: charge the energy storage device at a first charging rate when theenergy storage device is coupled to the first connection; charge theenergy storage device at a second charging rate when the energy storagedevice is coupled to the second connection; and operate the plurality ofDC converters when charging the energy storage device by: operating afirst DC converter to boost the input voltage to an intermediatevoltage; and operating a second DC converter to buck the intermediatevoltage to an output voltage to charge the energy storage device.
 2. Thevehicle charging system of claim 1, wherein at least one of theplurality of DC converters comprises an isolation transformer.
 3. Thevehicle charging system of claim 2, wherein the DC converter furthercomprises a rectifier coupled to the isolation transformer.
 4. Thevehicle charging system of claim 1, further comprising anelectromechanical device.
 5. The vehicle charging system of claim 4,further comprising an inverter coupled to the electromechanical device.6. The vehicle charging system of claim 1, wherein the first and secondconnection are each mating contacts.
 7. A vehicle comprising: an energystorage device; a connection system coupleable to an external chargingsource and configured to utilize a first connection and a secondconnection, the connection system configured to: provide an inputvoltage to charge the energy storage device at a first charging ratewhen the energy storage device is coupled to the first connection; andprovide an input voltage to charge the energy storage device at a secondcharging rate when the energy storage device is coupled to the secondconnection; and a plurality of DC converters coupleable to theconnection system, the plurality of DC converters configured to: boostthe input voltage to an intermediate voltage via a first DC converter;and buck the intermediate voltage to an output voltage via a second DCconverter, the output voltage for charging the energy storage device. 8.The vehicle of claim 7, wherein at least one of the plurality of DCconverters comprises an isolation transformer.
 9. The vehicle chargingsystem of claim 8, wherein the DC converter further comprises arectifier coupled to the isolation transformer.
 10. The vehicle of claim7, further comprising an AC motor.
 11. The vehicle of claim 10, furthercomprising an inverter coupled to the AC motor.
 12. The vehicle of claim7, wherein the first and second connection are each mating contacts. 13.The vehicle of claim 7, wherein the vehicle is a plug-in hybrid electricvehicle.
 14. A method for charging an energy storage device on-board avehicle, the vehicle including a connection system coupleable to anexternal charging source and a plurality of DC converters, the methodcomprising: providing an input voltage to charge the energy storagedevice at a first charging rate if the energy storage device is coupledto a first connection of the connection system; providing an inputvoltage to charge the energy storage device at a second charging rate ifthe energy storage device is coupled to a second connection of theconnection system; boosting the input voltage to an intermediate voltagevia a first DC converter of the plurality of DC converters; and buckingthe intermediate voltage to an output voltage via a second DC converterof the plurality of DC converters, the output voltage to charge theenergy storage device.
 15. The method of claim 14, further comprisingconfiguring a controller to control switching of the plurality of DCconverters such that the input voltage is suitable for charging theenergy storage device.
 16. The method of claim 14, wherein the first andsecond connection are each mating contacts.
 17. The method of claim 14,wherein the vehicle is a plug-in hybrid electric vehicle.